Delaware River and Bay Contaminants Strain Waterfowl Reproduction

Making the Nature Conservancy’s list of Last Great Places doesn’t guarantee a safe habitat. The osprey, a fish-feeding bird, nests along the Delaware River and Bay and continues to face contaminated living conditions. Although stable, osprey reproduction is stressed, according to an article published in the latest issue of Environmental Toxicology and Chemistry.

Ospreys and other wildlife share the Delaware River and Bay area with factories, manufacturers and water traffic using the Bay’s ports. The osprey population suffered substantial losses beginning in the 1950s with the widespread use of organochlorine pesticides. Contamination continued into the late 1980s when a study reported eggshell thinning and reproduction impairment mostly caused by p,p?-dichlorodiphenyldichloroethylene (p,p?-DDE). Using the same study sites, 1998 samples showed that contamination dropped off to levels where eggshell thickness was similar to the pre-DDT era.

In this study, researchers conducted the first large-scale ecotoxicological evaluation of ospreys nesting along the Delaware River, Bay and coast. Based on samples taken in 2002, they concluded that contaminant concentrations were predictive of hatching success. These contaminants included DDT, dieldrin, chlordane, polychlorinated biphenyls (PCBs) and dioxins to name a few.

Researchers also found that degradation of the River and Bay declined in a north-to-south gradient. In the research area’s northern segment, including Trenton, N. J., and Philadelphia, osprey eggs showed greater concentrations of organochlorine pesticides and/or metabolites as well as PCBs. Osprey reproduction in the north was marginal to maintain the population, researchers said. Farther down in the southern and central segments, reproduction was comparable to levels from 1994 to 1998.

Overall osprey population has not returned to its pre-1950s numbers, and the waterfowl is no longer considered a common breeder in the Delaware Bay area. The article’s research team emphasizes further study of nesting activity, breeding success, and contaminant exposure to evaluate human impact on urban wildlife. The osprey, the researchers said, serves as an excellent sentinel species and bioindicator of improving conditions in the coastal ecosystem.